During the first year of life, a well fed infant may triple its body mass. Consequently, this is a period of peak demand for arachidonic acid (ARA), a long chain polyunsaturated fatty acid (PUFA) that is a major structural lipid in peripheral and organ tissues. This is naturally provided to the infant in mother's milk since ARA is the most abundant C20-PUFA therein. However, commercial infant formulas available today are not supplemented with ARA or any other important long chain PUFAs. Recent studies using fish oil supplementation of pre-term infant formula to provide essential omega-3 PUFAs (specifically docosahexaenoic acid) for brain and retina development have resulted in a significant depression of plasma red blood cell ARA. Thus, a co-supplementation with an ARA-based oil may be warranted in this case. The goal of this research is to develop an additive for commercial infant formulas which will provide ARA and DHA levels equivalent to those in human breast milk. We have already isolated an ARA-producing microorganism which can be grown using conventional fermentation technologies. In Phase I, we shall optimize the production of this organism and determine the economic feasibility of using this approach to produce a fish oil/ARA oil supplement for infant formula. During Phase II, we shall prepare and test various formulas containing the additive.